KR102264546B1 - Electrode assembly for secondary battery - Google Patents

Abstract

The present invention relates to an electrode assembly, and particularly, in a lithium secondary battery including a multi-row stacked electrode, by including a current collector formed of a porous conductor in the electrode, resistance is reduced, and movement of lithium ions is smooth, so that output and lifespan It relates to an electrode assembly for a secondary battery having an improving effect.

Description

Electrode assembly for secondary battery {ELECTRODE ASSEMBLY FOR SECONDARY BATTERY}

The present invention relates to an electrode assembly, and particularly, in a lithium secondary battery including a multi-row stacked electrode, by including a current collector formed of a porous conductor in the electrode, the resistance is reduced, the movement of lithium ions becomes smooth, the output and It relates to an electrode assembly for a secondary battery having an effect of improving the lifespan.

With the increase in technology development and demand for mobile devices, there is an urgent need to develop a small, lightweight, long-lasting, and reliable high-performance small secondary battery. In addition, there is a growing demand for the development of electric vehicles, which are one of the solutions to environmental and energy problems, and large secondary batteries for efficient use of late-night idle power. In order to meet this demand, a lot of research has been done on lithium secondary batteries.

Lithium secondary batteries can be divided into lithium metal batteries and lithium ion batteries using an organic solvent electrolyte, and lithium polymer batteries using solid polymer electrolytes, depending on the type of electrolyte.

Of these, lithium polymer batteries have a solid electrolyte, so there is no concern about electrolyte leakage, so stability is secured. Also, they can be manufactured in various sizes and shapes with high energy density depending on the use, so continuous development is expected in the future. have.

On the other hand, as the number of charge and discharge increases in lithium secondary batteries, resistance components are generated at the interface between the positive electrode active material and the electrolyte, the negative electrode active material and the electrolyte, and the electrolyte itself, and the flow of lithium ions is disturbed, so the lifespan and capacity decrease. will do

In particular, the resistance component is mainly generated by the decomposition reaction of the electrolyte that occurs on the positive electrode side. The decomposition reaction of the electrolyte generates a lot of gas to reduce the contact inside the battery to increase the resistance, or to increase the viscosity of the electrolyte to increase the lithium ion It interferes with the flow of the battery, there is a problem that the life and capacity of the battery is reduced.

In relation to the present invention, although an electrode assembly is disclosed in Korean Patent Application Laid-Open No. 10-2013-011697 (published on October 11, 2013), technical means for solving the above problems are not mentioned.

An object of the present invention is to solve the resistance problem as described above, in a lithium secondary battery including a multi-row stacked electrode, resistance is reduced by including a current collector formed of a porous conductor in the electrode, and movement of lithium ions is smooth Thus, it is to provide an electrode assembly for a secondary battery having an effect of improving output and lifespan.

The present invention relates to a lithium secondary battery including a multi-row stacked electrode, by including a current collector formed of a porous conductor in the electrode, the resistance is reduced, the movement of lithium ions is smooth, and the output and lifespan are improved. An electrode assembly is provided.

According to the electrode assembly for a secondary battery of the present invention, the resistance applied to the entire electrode is lowered by including the multi-row stacked electrode, and the resistance is further reduced by including a current collector formed of a porous conductor in the electrode, and the movement of lithium ions is smooth. , it is possible to obtain the effect of improving the output and lifespan of the secondary battery.

1 is a cross-sectional view of an electrode assembly of the present invention.
2 is a cross-sectional view of the first electrode included in the electrode assembly of the present invention.
3 is a cross-sectional view of a second electrode included in the electrode assembly of the present invention.
4 is a cross-sectional view of a first electrode included in an electrode assembly according to another embodiment of the present invention.
5 is a cross-sectional view of an electrode assembly according to an embodiment of the present invention.
6 is a cross-sectional view of an electrochemical device including an electrode assembly according to an embodiment of the present invention.
7 is a cross-sectional view of another electrochemical device including an electrode assembly according to an embodiment of the present invention.

Advantages and features of the present invention, and methods for achieving them, will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in a variety of different forms, and only the present embodiment is intended to complete the disclosure of the present invention, and it is common knowledge in the art to which the present invention pertains. It is provided to fully inform those who have the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, an electrode assembly for a secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

The electrode assembly of the present invention includes a first electrode part, a second electrode part, and a separator separating the first electrode part and the second electrode part, wherein the first electrode part or the second electrode part is two or more units. Including an electrode, the current collector included in the first electrode portion or the second electrode portion is characterized in that the porous conductor.

1 is a cross-sectional view of an electrode assembly of the present invention.

As shown in FIG. 1 , the electrode assembly of the present invention includes a first electrode part 101 , a second electrode part 102 , and separating the first electrode part 101 and the second electrode part 102 . It is formed to include a separation membrane 103 .

In the present invention, as shown in FIGS. 2 and 3 , the first electrode part 101 or the second electrode part 102 may include two or more unit electrodes in order to lower the resistance applied to all electrodes. have.

First, the first electrode unit 101 will be described with reference to FIG. 2 .

In the present invention, the first electrode unit 101 may be an anode. The first electrode unit 101 includes a cathode active material layer 11 coated on both surfaces of the current collector 10 made of a thin metal plate (eg, aluminum foil) having excellent conductivity. As an active material, a chalcogenide compound is used, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _{1- x} Co _x O ₂ (0<x<1), LiMnO ₂ Composite metal oxides such as are used. , but the material is not limited in the present invention.

In the present invention, the first electrode unit 101 may include two or more unit electrodes 101-a and 101-b. As shown in FIG. 2 , when two or more unit electrodes are stacked in multiple rows, the resistance applied to the electrodes can be reduced in inverse proportion to the number of stacked electrodes.

The second electrode unit 102 will be described with reference to FIG. 3 .

In the present invention, the second electrode unit 102 may be a cathode. The second electrode unit 102 includes a negative electrode active material layer 12 coated on both sides of the current collector 20 made of a thin conductive metal plate (eg, copper or nickel foil). Carbon-based materials, Si, Sn, tin oxide, tin alloy composite, transition metal oxide, lithium metal nitride, lithium metal oxide, etc. are used as the active material, but the present invention is not limited thereto.

In the present invention, the second electrode unit 102 may include two or more unit electrodes 102-a and 102-b. As shown in FIG. 3 , when two or more unit electrodes are stacked in multiple rows, the resistance applied to the electrodes can be reduced in inverse proportion to the number of stacked electrodes.

In the present invention, the positive electrode current collector 10 or the negative electrode current collector 20 included in the first electrode part 101 or the second electrode part 102 is aluminum foil, copper foil, nickel foil, copper mesh, carbon mesh. It may be at least one selected from among. In particular, it is preferable that the negative electrode current collector has electronic conductivity while exhibiting electrochemical inactivity in the operating range of the carbon electrode (0.01 to 3V compared to lithium at the standard potential).

That is, in each electrode part, the current collector acts as a kind of channel so that lithium ions can actively move in the active material layer located inside the current collector among the multi-row stacked unit electrodes, the resistance is further reduced and , the movement of lithium ions becomes smooth, and the effect of improving the output and lifespan of the secondary battery can be obtained.

In the present invention, the transmittance of the porous conductor may be 45 to 95%, more preferably 60 to 85%. When the transmittance is less than 45%, the conductivity of lithium ions is low due to the low transmittance, which increases the resistance, and the output and lifespan of the secondary battery are inferior. When it exceeds 95%, the conductivity of lithium ions is increased due to the high permeability, but since the area occupied by the conducting wire of the porous conductor is reduced, the electronic conductivity is lowered and the characteristics of the secondary battery are deteriorated.

In the present invention, the average diameter of the pores of the porous conductor is preferably 300 nm to 900 nm, particularly 500 nm to 900 nm.

When the average diameter of the pores is less than 300 nm, the resistance increases and the life and output characteristics of the secondary battery are deteriorated, and when it exceeds 900 nm, there is a problem in securing a quantitative coating thickness due to the pores larger than the active material.

On the other hand, when two or more unit electrodes are stacked in multiple rows, interfacial resistance occurs at the interface between adjacent active material layers. In order to solve this problem, in the present invention, a conductive intermediate layer 15 is interposed between two or more unit electrodes stacked in multiple rows. It may include a configuration that

4 is a cross-sectional view of the first electrode part with the conductive intermediate layer 15 interposed between two or more unit electrodes stacked in multiple rows, taking the first electrode layer 101 as an example.

In the present invention, the conductive intermediate layer 15 is for solving the interfacial resistance that may be generated at the interface of the multi-row stacked electrodes, and is graphite, carbon nanotube, carbon black, acetylene black, Ketjen black, furnace black, carbon fiber, VGCF. It may be formed of a conductive paste including at least one conductive material selected from among.

Here, the viscosity of the conductive paste is preferably selected selectively according to the particle shape and surface state of the first electrode, that is, the positive electrode, and the solid content is also different according to the viscosity, so it can be prepared accordingly. Specifically, when the viscosity of the conductive paste is less than 100cp, the solid content is less than 35% by weight, when the viscosity is 100cp or more to less than 500, the solid content is 35 to 50% by weight, and when the viscosity is 500cp or more to 35000cp, the solid content is greater than 50% by weight.

Here, the content of the conductive material may be 98 parts by weight or more relative to 100 parts by weight of the conductive paste. When the content of the conductive material is less than 98 parts by weight, the resistance of the electrode interface increases as the content of the binder increases. That is, the content of the preferable conductive material capable of improving the binding force and conductivity with the electrode is 98 parts by weight or more.

Here, the binder for manufacturing the conductive paste may include at least one selected from PVDF, NMP, and CMC/SBR.

Here, the average particle size of the conductive material included in the conductive intermediate layer may be 10-50 μm excluding carbon nanotubes, and the specific surface area may be 30-15000 m ² /g. In the case of carbon nanotubes, the diameter may be 5 to 200 nm.

Here, the conductive material included in the conductive intermediate layer may be surface-treated to be well dispersed in the conductive paste. Specifically, a compound treated to include oxygen-containing groups on the surface of the conductive material may be used. In addition, in order to help disperse the conductive material, the binder in the conductive paste may include a dispersant or a dispersion medium.

Here, the thickness of the conductive intermediate layer may be 1 ~ 5㎛, more preferably 1 ~ 3㎛. The conductive intermediate layer is applied to minimize the interfacial resistance between electrodes of the same type. When the thickness of the conductive intermediate layer exceeds 5 μm, the ohmic resistance increases and thus the interface resistance increases. If the thickness is less than 1 μm, the conductive paste As the electrode permeates into the pores in the electrode and the binding force decreases, there is a problem in that resistance is also increased.

On the other hand, as shown in FIG. 5 , in the electrode assembly according to an embodiment of the present invention, a plurality of first electrode parts 101 and a plurality of second electrode parts 102 are alternately stacked, and the separator 103 is zigzag. It may have a shape in which the first electrode part 101 and the second electrode part 102 that are alternately stacked are separated from each other.

The first electrode part 101 and the second electrode part 102 are as described above, and the separator 103 is a configuration that separates the first electrode part 101 and the second electrode part 102, and is made of polyethylene, poly It may be made of any one selected from the group consisting of propylene and a copolymer of polyethylene and polypropylene, but the material is not limited in this embodiment.

In addition, the present invention may include an electrochemical device in which the electrode assembly described above is overlapped as a basic unit, and a separation film is interposed in each of the overlapping portions.

That is, as shown in FIGS. 6 and 7 , a first electrode unit 101 , a second electrode unit 102 , and a separator separating the first electrode unit 101 and the second electrode unit 102 . 103) and overlapping the electrode assembly of the present invention as a basic unit, the separation film 201 may be interposed in each of the overlapping portions.

Here, the separation film 201 is interposed at a different position from the separation film 103 , but the material and other configurations may be considered to be the same at a level acceptable to those skilled in the art.

Specifically, as shown in FIG. 6 , in the electrochemical device of the present invention, a plurality of electrode assemblies are alternately stacked, and a separation film 201 is formed in a zigzag shape to separate the alternately stacked electrode assemblies, respectively.

In addition, as shown in FIG. 7 , the electrochemical device of the present invention is manufactured by placing a plurality of electrode assemblies in a predetermined pattern on the separation film 103 and winding the separation film 103 , and the separation film 201 is an electrode. It may have a form in which the assemblies are separated from each other.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and cannot be construed as limiting the present invention in any sense.

Content not described here will be omitted because it can be technically inferred sufficiently by a person skilled in the art.

Example One

(anode manufacturing)

Li(Ni/Co/Mn)O2 : Carbon black : PVDF = 94 : 3 : After dispersing in NMP in a weight ratio of 3 to prepare a slurry, the slurry was coated on both sides on an aluminum foil having a porosity of 50%, 130 After drying sufficiently at ℃, a unit anode was prepared by pressing. The thickness of the double-coated anode was 140 μm.

(Cathode Manufacturing)

Graphite: acetylene black: PVDF = 93: 1: After preparing a slurry by dispersing in NMP in a weight ratio of 6, the slurry was coated on both sides on copper foil, dried sufficiently at 130 ° C., and pressed to prepare a unit cathode. The thickness of the double-coated negative electrode was 135 μm.

(Preparation of conductive intermediate layer)

After preparing a slurry by dispersing it in water at a weight ratio of furnace black: CMC/SBR = 98: 2, the slurry was coated on an anode-coated electrode within 1 to 5 μm to prepare a conductive intermediate layer. The coated area should be coated between facing homogeneous electrodes.

(Manufacture of electrode assembly)

A polypropylene film having a thickness of 16 μm having a microporous structure as a separator is used as the first polymer separator, and Solvey Polymer's polyvinylidene fluoride-chlorotrifluoroethylene copolymer 32008 is used as a gelling secondary polymer A multilayer polymer film was used.

The unit anode in which the cathode material prepared above is coated on both sides on the cathode current collector is cut into a rectangle with a size of 2.9 cm × 4.3 cm except for the place where the tab is to be made, and another unit cathode prepared in the same way is cut in the same way. Then, while overlapping the unit anodes, the prepared conductive intermediate layer was positioned at the interface between the unit anodes. In order to reduce the interfacial resistance, the conductive paste coated on the positive electrode was passed through a roll laminator at 140° C. and thermally fused to prepare a positive electrode assembly.

On the other hand, after cutting the negative electrode coated on both sides with the negative electrode material on the negative electrode current collector in a 3.0 cm × 4.4 cm rectangle except for the tab, the multilayer polymer film prepared above was placed between the positive electrode and the negative electrode by 3.1 cm. After being cut and positioned to a size of × 4.5 cm, it was passed through a roll laminator at 100° C. and each electrode and the separator were thermally fused and adhered to prepare the electrode assembly of FIG. 1 .

(Manufacturing of electrochemical devices)

The electrode assembly prepared above is overlapped as in the structure of FIG. 5, but the multilayer polymer film prepared above is positioned in a zigzag form on the overlapping portion of each electrode assembly, and then passes them through a roll laminator at 100 ° C. Each electrode assembly and the multilayer polymer film were thermally fused and adhered.

(battery manufacturing)

The prepared electrochemical device was put in an aluminum laminate packaging material, and EC/EMC/DEC/PC in LiPF6 was injected and then packaged.

Example 2

An electrode assembly, an electrochemical device, and a battery were manufactured in the same manner as in Example 1, but the conductive intermediate layer was not used at the interface between the unit anodes.

comparative example One

(anode manufacturing)

Li(Ni/Co/Mn)O2 : Carbon black : PVDF = 94 : 3 : After dispersing in NMP in a weight ratio of 3 to prepare a slurry, the slurry was coated on both sides on aluminum foil and dried sufficiently at 130 ° C. A unit anode was prepared by pressing. The thickness of the double-coated anode was 140 μm.

(Cathode Manufacturing)

Graphite: acetylene black: PVDF = 93: 1: After preparing a slurry by dispersing in NMP in a weight ratio of 6, the slurry was coated on both sides on copper foil, dried sufficiently at 130 ° C., and pressed to prepare a unit cathode. The thickness of the double-coated negative electrode was 135 μm.

(Manufacture of electrode assembly)

A polypropylene film having a thickness of 16 μm having a microporous structure as a separator is used as the first polymer separator, and Solvey Polymer's polyvinylidene fluoride-chlorotrifluoroethylene copolymer 32008 is used as a gelling secondary polymer A multilayer polymer film was used.

The positive electrode prepared above, the positive electrode material coated on both sides on the positive electrode current collector, was cut into a rectangle with a size of 2.9 cm × 4.3 cm except for the tab where the negative electrode material was coated on both sides on the negative electrode current collector, and the negative electrode material was coated on both sides on the negative electrode collector by 3.0 cm × 4.3 cm. After cutting the 4.4 cm rectangle except for the tab where the tab will be made, the multilayer polymer film prepared above was cut into a size of 3.1 cm × 4.5 cm between the positive electrode and the negative electrode and placed through a roll laminator at 100 ° C. Then, each electrode and the separator were heat-sealed and adhered to prepare an electrode assembly.

(Manufacturing of electrochemical devices)

The electrode assembly prepared above is overlapped as in the structure of FIG. 5, but the multilayer polymer film prepared above is positioned in a zigzag form on the overlapping portion of each electrode assembly, and then passes them through a roll laminator at 100 ° C. Each electrode assembly and the multilayer polymer film were thermally fused and adhered.

(battery manufacturing)

The prepared electrochemical device was put in an aluminum laminate packaging material, and EC/EMC/DEC/PC in LiPF6 was injected and then packaged.

comparative example 2

An electrode assembly, an electrochemical device, and a battery were manufactured in the same manner as in Example 1, but as a positive electrode current collector, a general aluminum foil in which pores were not formed was used.

evaluation

The lifespan and capacity of the batteries prepared in Examples and Comparative Examples were measured, and the results are shown in Table 1 below.

Life characteristics evaluation method:

Charge 2C, 4.2V (CC/CV), 0.1C cut off, rest 10min,

Discharge 2C, 2.5V(CV), rest 10min

After charging in the above manner, the cycle was performed until the discharge capacity deteriorated by 80% by setting the discharge capacity as one cycle.

Capacity characteristics evaluation method:

Charge 1C, 4.2V (CC/CV), 0.1C cut off, rest 10min,

Discharge 1C, 2.5V(CV), rest 10min

Discharge was performed in the same manner as above to confirm the capacity characteristics.

EOL 80% Example 1 Example 2 Comparative Example 1 Comparative Example 2 life (cycle) 1040 1039 748 1260 Capacity (mAh) 870 867 832 863

From the above results, in the case of Comparative Example 1, it can be seen that compared to Examples 1 and 2, the life characteristics and capacity characteristics are significantly lowered. This is because a large amount of resistance was generated in the anode of Comparative Example 1. In addition, even if the positive electrode is laminated in multiple rows to reduce resistance, when the porous conductor is not used as the current collector as in Comparative Example 2, the movement of lithium ions in the active material layer located inside is not smooth. The capacity characteristics were not excellent.

That is, according to the electrode assembly for a secondary battery of the present invention, the resistance applied to the entire electrode is lowered by including the multi-row stacked electrode, and the resistance is further reduced by including a current collector formed of a porous conductor in the electrode, and the movement of lithium ions is smooth As a result, it can be confirmed that the output and lifespan of the secondary battery are improved.

In the above, the embodiments of the present invention have been mainly described, but various changes or modifications can be made at the level of those skilled in the art to which the present invention pertains. Such changes and modifications can be said to belong to the present invention as long as they do not depart from the scope of the technical spirit provided by the present invention. Accordingly, the scope of the present invention should be judged by the claims described below.

Claims (13)

In an electrode assembly comprising a first electrode part, a second electrode part, and a separator separating the first electrode part and the second electrode part,
The first electrode part or the second electrode part includes two or more unit electrodes stacked in multiple rows,
The unit electrode includes a current collector and an active material layer disposed on both sides of the current collector,
The current collector included in the first electrode part or the second electrode part is a porous conductor,
An electrode assembly, characterized in that a conductive intermediate layer is interposed at the interface between the unit electrodes.
The method of claim 1,
The porous conductor is an electrode assembly, characterized in that at least one selected from aluminum foil, copper foil, nickel foil, copper mesh, and carbon mesh.
The method of claim 1,
The electrode assembly, characterized in that the transmittance of the porous conductor is 45 to 95%.
delete The method of claim 1,
The conductive intermediate layer is formed of a conductive paste comprising at least one conductive material selected from graphite, carbon nanotube, carbon black, acetylene black, Ketjen black, furnace black, carbon fiber, and VGCF.
6. The method of claim 5,
An electrode assembly, characterized in that compared to 100 parts by weight of the conductive paste, the content of the conductive material is 98 parts by weight or more.
6. The method of claim 5,
The electrode assembly, which is included in the conductive intermediate layer, has an average particle size of 10-50 μm and a specific surface area of 30-15000 m ² /g of a conductive material excluding carbon nanotubes.
6. The method of claim 5,
The electrode assembly, characterized in that the average particle diameter of the conductive material included in the conductive intermediate layer, which is carbon nanotubes, is 5 to 200 nm.
6. The method of claim 5,
The conductive material included in the conductive intermediate layer is an electrode assembly, characterized in that the surface treatment.
6. The method of claim 5,
The electrode assembly, characterized in that the thickness of the conductive intermediate layer is 1 ~ 5㎛.
The method of claim 1,
The first electrode part is an anode, and the second electrode part is an electrode assembly, characterized in that the cathode.
The method of claim 1,
A plurality of the first electrode parts and a plurality of the second electrode parts are alternately stacked,
The separator is formed in a zigzag shape to separate the alternately stacked first and second electrode parts, respectively.
An electrochemical device in which the electrode assembly of claim 1 is overlapped as a basic unit, and a separation film is interposed in each of the overlapping portions.

Images